Power train

ABSTRACT

Power train ( 20 ) or an amphibious vehicle comprises engine ( 8 ), transmission ( 9 ), and transfer case ( 13 ) position in-line with longitudinal vehicle axis (A), (FIG.  2 ), towards the rear of the vehicle, with transmission output ( 11 ) facing the front of the vehicle. The transfer drive drives the rear wheels via propeller shaft ( 15 ), which extends adjacent the engine to rear differential ( 6 ). A marine drive PTO (power take off) may be taken from a shaft from the transfer case ( 37 ), (FIGS.  6  to  10 ), from the propeller shaft ( 15 ) (FIG.  4 ), or from engine crankshaft pulley ( 2 ). Marine drive shaft ( 3 ) (FIGS.  6  to  10 ) may run below the engine, or alongside it, on the opposite side of the engine from propeller shaft ( 15 ). Decouplers ( 4, 24, 26; 38, 40, 41 ) may be provided to the PTO drive, to at least one rear wheel, and on the optional front axle propeller shaft ( 16 ).

[0001] This invention relates to a power train which is particularlysuitable for use in an amphibious vehicle capable of travel on land andwater, and more particularly to an adaptation of a conventionalautomotive power train having an in-line engine and speed changetransmission to drive both the rear wheels and the marine propulsionunit of an amphibious vehicle. The invention also relates to anamphibious vehicle having such a power train.

[0002] In a known automotive power train arrangement for a conventionalland based vehicle, an engine and speed change transmission arepositioned at the front of the vehicle in-line with the longitudinalaxis of the vehicle. The driving end of the transmission faces the rearof the vehicle, and is connected by a drive shaft, otherwise known as apropeller shaft, to a rear differential for driving the rear wheels ofthe vehicle.

[0003] It is also known to use an in-line engine and speed changetransmission to drive the wheels and marine propulsion unit of anamphibious vehicle. For example U.S. Pat. No. 4,958,584 (Williamson)discloses a power train arrangement in which the engine and transmissionare located at the rear of the vehicle, with the driving end of thetransmission facing the front of the vehicle. A propeller shaft providesdrive from the transmission to a front differential for driving thefront wheels of the vehicle. The rear wheels of the vehicle are notdriven. A marine propulsion unit is positioned behind the engine, and isdriven from the timing end of the crank shaft of the engine. Thisarrangement is best seen in FIG. 5 of U.S. Pat. No. 4,958,584.

[0004] U.S. Pat. No. 4,838,194 (Williamson) is the parent application toU.S. Pat. No. 4,958,584 above. This patent also discloses an amphibiousvehicle having a power train arrangement in which an in-line engine andtransmission appear to be located at the rear of the vehicle, with thedriving end of the transmission facing the front of the vehicle. Thefront wheels are driven by a shaft from a transfer case which alsoprovides drive to a rearward facing marine drive.

[0005] The marine drive has a long, propeller shaft to a screwpropeller, both of which along with a rudder, can be raised for roaduse; and lowered for marine use. The arrangement leaves little roomanywhere in the vehicle for an engine and speed change transmission; thelocation of which is not specifically disclosed.

[0006] If the engine and transmission are located behind the vehiclerear axle (as in the case in the continuation in part U.S. Pat. No.4,958,584), they would either have to be located above the propellershaft, raising the centre of gravity to the detriment of vehiclehandling on land and water; or to one side of the propeller shaft,giving odd weight distribution, and packaging problems. Either of theseoptions would need a skewed drive to the transfer box, leading to powerlosses and possible NVH (noise, vibration, and harshness) problems. Itshould also be noted that the long vertically adjustable propeller shaftwould give rise to sealing problems in the bottom of the hull, whichcould lead to water ingress and corrosion problems in the transfer case.Altogether, this does not appear to be a practical layout for anamphibious vehicle.

[0007] European patent No EP 0 341 009 (Royle) shows a further exampleof an amphibious vehicle in which an in-line engine and transmission areprovided at the rear of the vehicle, with the output of the transmissionfacing the front of the vehicle. In this layout, the transmission drivesthe rear wheels of vehicle via a drive shaft, whilst a marine propulsionunit, located behind the engine, is driven from the timing end of theengine.

[0008] There are significant disadvantages in the above known amphibiousvehicle power train arrangements, especially in the light of the highdemands which are required of a modern vehicle in road operation asdiscussed below.

[0009] When a vehicle accelerates in a forward direction, the front ofthe vehicle tends to lift upwards in reaction to the rotationalacceleration of the wheels relative to the vehicle. This happensirrespective of whether the vehicle is front or rear wheel drive and canlead to a loss of traction between the front wheels and the road underacceleration. This problem is exaggerated in the known amphibiousvehicle arrangements where the engine is positioned behind the rearwheels of the vehicle. This is because the weight of the engine whenpositioned behind the rear wheels adds to the lifting force; as opposedto a conventional power train arrangement with the engine at the frontof the vehicle, where the engine weight would counteract the liftingforce. Consequently, in the known amphibious vehicle arrangements, thefront wheels will tend to lose traction under acceleration. In practicethis causes excessive wheel spin and tire wear. This is a particularproblem in the Williamson layouts in which the vehicle is front wheeldrive.

[0010] Furthermore, when a vehicle leaves a bend, the adhesion betweenthe tyre and road surface must resist both acceleration and centrifugalforces. If the combination of these forces approaches or goes beyond thetractive limits of the front tyres, an under-steer condition will occur.In the conventional land based vehicle power train arrangementspreviously mentioned, the weight of the engine is positioned at thefront of the vehicle, which reduces the tendency to under-steer whencornering. However, in the known amphibious vehicle arrangements inwhich the weight of the engine is behind the rear wheels, there will bea reduction in the load on the front wheels which increases thelikelihood of under-steer occurring.

[0011] It is also known to provide for four wheel drive capability inconventional land based automotive vehicles having an in-line engine andspeed change transmission located at the front of the vehicle. In sucharrangements, the output end of the transmission faces the rear of thevehicle and a transfer case is used to selectively drive the rear wheelsonly or the front and rear wheels.

[0012] It has been proposed to use an automotive power train of thistype to drive an amphibious vehicle, using the rear wheel drive to drivethe marine propulsion unit and the front wheel drive to drive the frontwheels. In order to use the power train in this way, it is necessary tolocate the engine and transmission in the conventional position, towardsthe front of the vehicle.

[0013] Owing to rearward weight bias requirement for travel on water inan amphibious vehicle, it has been found unsuitable to locate the engineand transmission in this conventional position. It has also been found,contrary to the teachings in the Williamson patents, to be unsuitable todrive only the front wheels of an amphibious vehicle from a rear ormid-mounted engine, because the weight of the engine is not over thedriving wheels. This limits traction on wet slipways, leading toproblems leaving water; and can lead to wheel spin and rapid tyre wearon the road.

[0014] It is an object of the present invention to provide a power trainfor an amphibious vehicle in which a conventional in-line engine andspeed change transmission are utilised and in which the abovedisadvantages are reduced or substantially obviated.

[0015] In accordance with a first aspect of the present invention, thereis provided a power train for an amphibious vehicle comprising anin-line engine and speed change transmission assembly adapted such thatthe engine can be positioned towards the rear of the vehicle with thetransmission output facing the front of the vehicle, the power trainalso comprising a power take off means adapted to drive a marinepropulsion unit located behind the engine, characterised in that atransfer drive is provided in-line with the transmission, the transferdrive being adapted to drive the rear wheels of the vehicle via a firstdrive shaft which extends adjacent to the engine such that the enginecan be positioned at least partially forward of the rear wheels of thevehicle.

[0016] In a particularly preferred embodiment, the power train isadapted so that the engine is mounted between the rear wheels and thefront wheels of the vehicle.

[0017] In one preferred embodiment the power take off is provided by thetransfer box which drives the marine propulsion unit by means of asecond drive shaft which runs substantially parallel to and below theengine. Alternatively, the second drive shaft could run substantiallyparallel to and along one side of the engine. In this latterarrangement, it is preferable if the first drive shaft runs along anopposite side of the engine to the second drive shaft.

[0018] In an alternative preferred embodiment, the power take off isdriven by the engine crankshaft at the timing end of the engine.

[0019] In a yet further alternative preferred embodiment, the power takeoff comprises a further transfer drive which is fitted to, and drivenby, the first drive shaft.

[0020] The marine propulsion unit may be a water jet, or a marine screwpropeller. A decoupler may be provided in the drive line from the powertake off to the marine propulsion unit, to enable drive to the marinepropulsion unit to be selectively coupled and decoupled.

[0021] Preferably, the first drive shaft is adapted to drive the rearwheels of the vehicle via a rear differential. Where a four wheel drivecapability is required, the transfer drive can also drive a third driveshaft which is adapted to drive the front wheels of the vehicle througha front differential.

[0022] In an advantageous embodiment, a decoupler is provided in thedrive line between the transmission and at least one of the driven roadwheels, such that drive to the at least one driven wheel can beselectively coupled or decoupled.

[0023] Where a decoupler is provided for coupling drive to a wheel driveshaft, the decoupler may incorporate a synchromesh mechanism and may becombined with a constant velocity joint.

[0024] In accordance with a second aspect of the invention, there isprovided amphibious vehicle having a power train in accordance with thefirst aspect of the invention.

[0025] Several embodiments of the invention will now be described, byway of example only, with reference to the following drawings in which:

[0026]FIG. 1 is a perspective view of a first embodiment of a powertrain for an amphibious vehicle in accordance with the invention, inwhich a power take off is connected to a crankshaft pulley of theengine;

[0027]FIG. 2 is plan view of the power train of FIG. 1;

[0028]FIG. 3 is side view, partially in section, of a modified form ofthe power train of FIGS. 1 and 2;

[0029]FIG. 4 is a perspective view of a second embodiment of a powertrain in accordance with the invention, in which a power take off isconnected to a first drive shaft driving a rear differential of thevehicle; and

[0030]FIG. 5 is a plan view of the power train of FIG. 4;

[0031]FIG. 6 is a perspective view of a third embodiment of a powertrain for an amphibious vehicle in accordance with the invention;

[0032]FIG. 7 is a plan view of the power train of FIG. 6;

[0033]FIG. 8 is a side view, partially in section, of the power train ofFIG. 6;

[0034]FIG. 9 is a plan view of a fourth embodiment of a power train foran amphibious vehicle in accordance with the invention; and

[0035]FIG. 10 is a side view, partially in section, of the power trainof FIG. 9.

[0036] Common reference numbers have been used throughout the drawingsto denote parts in common between the different embodiments.

[0037] Referring firstly to FIGS. 1 to 3, a power train for use in anamphibious vehicle is generally indicated at 20, and includes alongitudinal power train assembly comprising an engine 8 and speedchange transmission or gearbox 9 arranged in-line with the longitudinalaxis of the vehicle A. The timing end 10 of the engine is locatedtowards the rear of the vehicle and the output from the transmissionfaces the front of the vehicle.

[0038] A transfer drive 13 is fitted in-line at the output end 11 of thetransmission 9 and transfers drive from the transmission 9 to acountershaft 14, the axis of which is offset relative to thelongitudinal axis A of the engine 8 and transmission 9. The countershaft14 is coupled to a first drive shaft 15, in the form of a propellershaft, which runs parallel to and along one side of the engine 8 todrive a rear differential 6. The differential 6 provides drive to theright hand side (as viewed in FIG. 1) rear wheel of the vehicle via arelay shaft 7 and a further drive shaft 12, whist the differential 6drives the left hand (as viewed) rear wheel via a drive shaft 18.

[0039] A decoupler or decouplers (not shown) may be provided in thedrive line between the transmission and at least one of the driven roadwheels to selectively decouple drive to the wheels when the vehicle isin marine mode. For example, a decoupler could be provided between thecounter shaft 14 and the first drive shaft 15. Alternatively, adecoupler or decouplers could be provided between the differential 6 andone or both of the rear wheels. In this latter arrangement, the or eachdecoupler could be provided between the differential 6 and a wheel driveshaft 12, 18, or between a wheel drive shaft 12, 18 and its respectiverear wheel. Where a decoupler is used to decouple drive to a wheel driveshaft 12, 18, the decoupler may be of the type which incorporates asynchromesh mechanism and is combined with a constant velocity joint.Such a decoupler is disclosed in the applicant's co-pendingInternational patent application No. PCT/GB01/03493, the contents ofwhich are hereby incorporated by reference.

[0040] A power take off for driving a marine propulsion unit 5 locatedbehind the engine is driven by the engine crankshaft at the timing endof the engine. In the present embodiment, the power take off is providedin the form of a coupling 1 which is fitted to, and is driven by, acrankshaft pulley 2 of the engine 8. The crankshaft pulley 2 being atthe timing end of the engine 8. A second drive shaft 3 is connected atone end to the coupling 1 and at the other end to a decoupler 4 whichselectively couples and decouples drive from the second drive shaft 3 tothe marine propulsion unit 5. The marine propulsion unit may be a waterjet or marine screw propeller.

[0041] In circumstances where a pulley is not provided at the timing endof the crankshaft, the power take off may be connected to the timing endof the crankshaft by any suitable means. For example, the power take offcould be connected to a sprocket provided at timing end of thecrankshaft, or the power take off may be connected directly to thetiming end of the crankshaft as appropriate.

[0042] In the arrangement shown, the relay shaft 7 which drives theright hand rear wheel is located between the engine 8 and the marinepropulsion unit 5. The relay shaft 7 can be positioned below the seconddrive shaft 3, as shown in FIGS. 1 and 2, or above the second driveshaft 3, as shown in FIG. 3, depending on the vehicle layout.

[0043] Where a four wheel drive capability is required, the countershaft 14 can be connected to a third drive shaft 16 which drives thefront wheels (not shown) via a front differential 17. A decoupler ordecouplers (not shown) may be provided in the drive line between thecounter shaft 14 and the differential 17, or between the differential 17and either or both of the front wheels, in order that drive to the frontwheels can be selectively coupled and decoupled.

[0044] A second embodiment of the invention will now be described withreference to FIGS. 4 and 5. An engine 8, transmission 9 and transferdrive 13 are arranged in the same manner as in the first embodimentdescribed above, with a first drive shaft 15 driving a rear differential6 from the transfer drive 13.

[0045] However, in this embodiment, the power take off is provided by afurther transfer drive 22, which transfers drive from the first driveshaft 15 to the second drive shaft 3 for driving a water jet 5. Adecoupler 4 selectively couples and decouples the drive from the seconddrive shaft 3 to the water jet 5. The further transfer drive 22transfers drive from the propeller shaft by means of a belt or chain,although it would be possible to transfer the drive using gears.

[0046] One or more decouplers 24, 26 are provided in the drive line fromthe differential 6 to the rear wheels to allow selective decoupling ofdrive to the road wheels while the vehicle is in marine mode. In aparticularly preferred embodiment, the decouplers 24, 26 are providedinboard of CV joints 28 and 30 also provided in the drive line. Wherespace in the vehicle is at a premium, the decouplers 24, 26 could be ofthe type, discussed above, which incorporate a synchromesh mechanism andwhich are combined with a CV joint. In such an arrangement, the separateCV joints 28, 30 will not be required. As an alternative to providingdecouplers in the drive line between the differential 6 and the rearwheels, one or more decouplers may be incorporated into or ahead ofdifferential 6 or into the transfer drive 22.

[0047] Where a four wheel drive capability is required then this can beprovided in the same manner as has been described above in relation tothe first embodiment.

[0048] A third embodiment of the invention will now be described withreference to FIGS. 6 to 8. The power train 50 comprises an engine 8 andtransmission 9 arranged in-line with the longitudinal axis of thevehicle. The engine is mounted toward the rear of vehicle with theoutput end 11 of the transmission 9 facing the front of the vehicle. Atransfer drive 13 is fitted to the output end 11 of the transmission 9and comprises a driving sprocket 18 which is drivingly coupled with anoutput shaft 42 of the transmission 9. The driving sprocket 18 isconnected in driving engagement by means of a drive belt 32 with a firstdriven sprocket 34, which is mounted to a first counter shaft 14, and asecond driven sprocket 36 mounted to a second counter shaft 37.

[0049] The first counter shaft 14 is connected via a decoupler 38 to afirst drive shaft 15 which drives a rear differential 6. The reardifferential 6 with a relay shaft 7 is located at the rear of the engine8 for driving the rear wheels (not shown) of the vehicle.

[0050] The second counter shaft 37 is connected via a decoupler 40 to asecond drive shaft 3. The second drive shaft 3 runs beneath the engine 8to the rear thereof, for connection to a marine propulsion unit 5, forexample a water jet.

[0051] As with the previous embodiments, a four wheel drive capabilitycan be provided by connecting the first counter shaft 14 to a thirddrive shaft 16 for driving the front wheels via a front differential 17.As shown, the first counter shaft is connected to the third drive shaft16 by a decoupler 41, so that drive to the front wheels can beselectively coupled and decoupled.

[0052] A fourth embodiment of the invention is shown in FIGS. 9 and 10.The fourth embodiment is substantially identical to the third embodimentexcept that the second drive shaft 3, which drives the marine propulsionunit 5, is arranged to run along one side of the engine 8 rather thanbelow the engine. In the embodiment shown, the second drive shaft 3 runsalong the opposite side of the engine from the first drive shaft 15,alongside the lower part of the cylinder block, below the cylinder bank.This arrangement enables the engine to be positioned lower in thevehicle, resulting in a lower centre of gravity which improves thehandling characteristics of the vehicle in water and on land.

[0053] In a power train in accordance with the invention where the firstdrive shaft 15 is driven from the transmission through a transfer box,the axis of the first drive shaft is offset relative to the longitudinalaxis of the engine 8 and transmission 9. Consequently, it is possible toposition the engine and transmission just in front of the rear wheelsand run the drive shaft 15 along one side of the engine to drive therear differential 6 and the rear wheels. This arrangement overcomes manyof the problems associated with the known amphibious vehicle power trainlayouts in which an in-line engine and transmission are located behindthe rear wheels. With the engine located just in front of the rearwheels, the weight of the engine and transmission help to counterbalance lift of the front of vehicle during acceleration. Furthermore,the centre of gravity of the vehicle is moved forward toward the centreof the vehicle, when compared with the prior art arrangements, whichimproves road holding and manoeuvrability of the vehicle on land.However, the engine and transmission are still located generally towardsthe rear of the vehicle which provides a more favourable weightdistribution for travel of the vehicle on water.

[0054] In alternative embodiments (not shown), the engine 8 could bemounted so that only a part of the engine is located forward of the rearwheels. This may be advantageous in providing more room for passengersbut without positioning the engine behind the rear axle as in the knownarrangements. However, it is advantageous if the whole engine is locatedbetween the front and rear wheels because then the engine can be mountedlower in the vehicle. This lowers the centre of gravity of the vehiclewhich improves vehicle handling as described above.

[0055] Whereas the invention has been described in relation to what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not limited to thedisclosed arrangements but rather is intended to cover variousmodifications and equivalent constructions included within the spiritand scope of the invention. For example, it is not essential that drivebetween the power take off and the marine propulsion unit be connectedvia a decoupler. Furthermore, the first drive shaft 15 could be arrangedto extend beneath the engine 8 rather than along one side.

1. A power train for an amphibious vehicle comprising an in-line engineand speed change transmission assembly adapted such that the engine canbe positioned towards the rear of the vehicle with the transmissionoutput facing the front of the vehicle, the power train also comprisinga power take off means adapted to drive a marine propulsion unit locatedbehind the engine, characterised in that a transfer drive is providedin-line with the transmission, the transfer drive being adapted to drivea first drive shaft which extends rearwardly along one side of, orbeneath the engine and which is adapted to drive a rear differential fordriving the rear wheels of the vehicle, the arrangement being such thatthe engine can be positioned at least partially forward of the rearwheels.
 2. A power train as claimed in claim 1, adapted such that theengine can be positioned between the rear wheels and the front wheels ofthe vehicle.
 3. A power train as claimed in claim 1 or claim 2, in whichthe power take off is provided by the transfer box which is adapted todrive the marine propulsion unit by means of a second drive shaft whichruns substantially parallel to and below the engine.
 4. A power train asclaimed in claim 1 or claim 2, in which the power take off is providedby the transfer box which is adapted to drive the marine propulsion unitby means of a second drive shaft which runs substantially parallel toand along one side of the engine.
 5. A power train as claimed in claim4, in which the first drive shaft runs along an opposite side of theengine to the second drive shaft.
 6. A power train as claimed in claim 1or claim 2, in which the power take off is driven by the enginecrankshaft at the timing end of the engine.
 7. A power train as claimedin claim 1 or claim 2, in which the power take off comprises a furthertransfer drive which is fitted to, and driven by, the first drive shaft.8. A power train as claimed in any previous claim in which the marinepropulsion unit is a water jet, or a marine screw propeller.
 9. A powertrain as claimed in any previous claim, in which a decoupler is providedin the drive line from the power take off to the to the marinepropulsion unit, to enable drive to the marine propulsion unit to beselectively coupled and decoupled.
 10. A power train as claimed in anyprevious claim in which the first drive shaft is adapted to drive therear wheels of the vehicle via a rear differential.
 11. A power train asclaimed in claim 10, in which the transfer drive also drives a thirddrive shaft which is adapted to drive the front wheels of the vehiclethrough a front differential.
 12. A power train as claimed in anyprevious claim, in which a decoupler is provided in the drive linebetween the transmission and at least one of the driven road wheels,such that drive to the at least one driven wheel can be selectivelycoupled or decoupled.
 13. A power train as claimed in claim 12 in whichthe at least one decoupler is arranged for coupling drive to a wheeldrive shaft, the decoupler incorporating a synchromesh mechanism andbeing combined with a constant velocity joint.
 14. A power trainsubstantially as hereinbefore described with reference to and asillustrated in FIGS. 1 to 3, or FIGS. 4 and 5, or FIGS. 6 to 8, or FIGS.9 and 10 of the accompanying drawings.
 15. An amphibious vehiclecharacterised in that the vehicle comprises a power train as claimed inany one of claims 1 to 14.